In a new study published in British Journal of Ophthalmology, researchers reported an epidemiological update on bacterial keratitis (BK) patterns in a tertiary ophthalmology center over 20 months compared with a previous study on the same timeframe from 1998 to 1999. They found that contact lens wear remained the leading risk factor for the condition but the prevailing organisms shifted to a predominance of Gram-negative bacteria and increased Moraxella spp. over 20 years.

A case of Moraxella keratitis. Authors of this study suggest eyecare practitioners should make contact lens hygiene a priority with patients to help reduce the risk of bacterial keratitis. Photo: Chris Sindt, OD. Click image to enlarge.

A total of 354 patients with BK documented by microbiological corneal scraping or resolution under antibiotic treatment from January 2020 to September 2021 were analyzed.

At least one common risk factor was found in 95.2% of patients: contact lens wear (45.2%), ocular surface disease (25.0%), systemic disease (21.8%), ocular trauma (11.9%) and ocular surgery (8.8%). The positivity rate of corneal scrapings was 82.5%, with 18.2% deemed polybacterial in nature. Gram-negative bacteria represented 59.9% of cases and the remaining 40.1% were gram-positive.

Poor visual prognosis was associated with older age, larger infiltrate size, ocular surface disease, ocular trauma and contact lens wear. Gram-negative bacteria were responsible for deeper and more extensive infiltrates in younger patients. Compared with the previous period, the positivity rate of corneal scrapings and the proportion of Gram-negative bacteria, especially Moraxella, increased.

The most common bacteria were Pseudomonas aeruginosa (32.5%), Moraxella (18.1%) and Staphylococcus aureus (8.2%). The authors found only three antibiotic-resistant P. aeruginosa (one to piperacillin, one to ceftazidime and one to gentamicin) and no MRSA, similar to the very low MRSA rate of 0.07% to 1% in the UK.

“All Moraxella spp. were sensitive, as in the study by Termote et al. in Vancouver,” the authors noted in their BJO paper. “The systematic use of three fortified topical antibiotics (i.e., piperacillin (20 mg/mL), gentamicin (15mg/mL) and vancomycin (50mg/mL)) for severe keratitis and the frequent use of topical quinolones in combination with another antibiotic could explain this low rate.”

All P. aeruginosa and Moraxella were sensitive to quinolones, and all S. aureus were sensitive to both quinolones and methicillin.

In the contact lens group, patients were younger, consulted quickly, had a better visual prognosis and had more Gram-negative species, especially P. aeruginosa, compared with the other groups. The high rate of contact lens wear may explain the high rate of P. aeruginosa, the authors noted, as lens wear induces hypoxia and hypercapnia of the cornea, making these eyes more susceptible to infection. “Mechanisms of biofilm formation, epithelial disruption and alteration of the antimicrobial quality of the tear film also favor the development of BK,” the authors explained in their article.